Electrophotographic photosensitive member

ABSTRACT

AN ELECTROPHOTOGRAPHIC PHOTOSENSITIVE MEMBER IS COMPOSED ESSENTIALLY OF A SUPPORT, A PHOTOCONDUCTIVE LAYER AND AN INSULATING LAYER, AND THE PHOTOCONDUCTIVE LAYER BEING COMPOSED OF A SELENIUM LAYER AT THE SUPPORT SIDE AND A SELENIUM-TELLURIUM LAYER AT THE INSULATING LAYER SIDE.

y 23, 1974 NOBUO KITAJIMA ET AL 3,813,243

ELECTROPHOTOGHRAPHIC PHOTOSENS ITIVE MEMBER Filed July 10. 1972 my v FIG.3

on w t N FIG4 United States Patent US. Cl. 96-1-5 1 Claim ABSTRACT OF THE DISCLOSURE An electrophotographic photosensitive member is composed essentially of a support, a photoconductive layer and an insulating layer, and the photoconductive layer being composed of a selenium layer at the support side and a selenium-tellurium layer at the insulating layer side.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to an electrophotographic photosensitive member essentially composed of a support, a photoconductive layer and an insulating layer and more particularly, to such an electrophotographic photosensitive member having a photoconductive layer of an Se-Te alloy.

Description of the prior art Many photosensitive members have been known and developed in the field of electrophotography. It is also known that, for example, Se ZuO and CdS can be used as a photoconductive layer in electrophotographic process.

These photoconductive materials should be appropriately selected for each different electrophotographic process.

The electrophotographic photosensitive member of the present invention is most suitable for an electrophotographic process as disclosed in US. Pat. 3,666,363. This electrophotographic process utilizes a photosensitive plate comprising a photoconductive layer and an insulating layer overlying the photoconductive layer. The process comprises applying a primary charge of a polarity to charge the insulating layer and simultaneously inject a charge of a polarity opposite to that of the primary charge from the support side, thereby binding the charge near the interface between the insulating layer and the photoconductive layer, then exposing to a light image simultaneously with applying a secondary charge of a polarity opposite to the primary charge or an electric field capable of eliminating the primary charge to release the charge at light portion of a projected image, thereby producing an electrostatic image and further applying a blanket irradiation to enhance the contrast.

In the above mentioned electrophotographic process, the state of charge injected from the support side, the state of charge bound near the interface between the insulating layer and the photoconductive layer, light sensitivity and contrast affect the formation of image to a great extent. These factors are largely dependent upon properties of a photoconductor itself and therefore,

it it a great problem to select an appropriate photoconductive layer.

Heretofore, photosensitive members composed of Se or Se-Te alloy have been already known which have high response to light, sensitivity and contract. For example, US. Pat. No. 2,803,541 discloses such photoconductive 3,813,243 Patented May 28, 1974 member. However, such conventional photosensitive member has only a photoconductive layer, but not any insulating layer, and therefore, the prior art teaches an optimum condition with respect to sensitivity and contrast only. Nothing of effect concerning injection and binding is not taken into consideration in the prior art. A photosensitive member composed of an Se-Te alloy layer and an insulating layer is also known, but the insulating layer is used only as a protecting layer for the photoconductive layer. Effect of retention of charge in the insulating layer is not disclosed at all.

SUMMARY OF THE INVENTION According to the present invention, there is provided an electrophotographic photosensitive member composed essentially of a support, a photoconductive layer and an insulating layer, and the photoconductive layer being composed of a selenium layer at the support side and a selenium-tellurium layer at the insulating layer side.

An object of this invention is to provide a photosensitive member in which the injection from the support can be effectively conducted.

Another object of this invention is to provide a photosensitive member in which the binding can be elfectively conducted.

A further object of this invention is to provide a photosensitive member having excellent sensitivity and contrast.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an enlarged cross sectional view of a photosensitive member having an Se rectifying layer on a support;

FIG. 2 is an enlarged cross sectional view of a photosensitive member having an insulating layer;

FIG. 3 shows a charging curve when charging is applied to the photosensitive member of FIG. 1; and

FIG. 4 shows a charging curve when charging is applied to the photosensitive member of FlIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The photoconductive layer in the present invention may be produced by vapor-depositing Se on a support and then Se-Te alloy on the resulting Se layer. This structure facilitates injection of carrier from the support and remarkably enhances the sensitivity.

Se layer on the support is preferably 0.01 to 5 microns thick, particularly preferred with 0.1 to 1 micron thick and Se-Te alloy layer (Te being preferably 6 to 45% by weight) overlying the Se layer is preferably 30 to 150 microns thick.

The following example is given for illustrating the present invention, but not for limiting thereof.

EXAMPLE Selenium (99.999% in purity) and tellurium (99.999% in purity) of 15% by weight based on selenium were placed in a Pyrex glass ampoule and vacuum sealed. Then the ampoule was maintained at 550 C. for 4 hours with stirring followed by quenching to produce an Se-Te alloy. This alloy is called a hereinafter.

This a (40 g.) was placed in a quartz tray and vaporized in vacuum (1 X 10- mm. Hg) by radiant heat from a tungsten wire for depositing on an aluminum support washed with supersonic wave in thickness of about 60 microns. Temperature of the support was maintained at 65 C. for min. and then quenched. The resulting aluminum support was taken out (hereinafter called Sample A-l).

Another sample (called hereinafter Sample B-l) prepared by adhering a polyethylene terephthalate film 3 of 25 microns thick onto a surface of the resulting photoconductive layer surface with an adhesive.

Further, Se (99.999% in purity) was vapor-deposited on an aluminum support by using a molybdenum boat at 30 cm. of a distance between the vapor source and the support and then the above mentioned a with different ratio of Se to Te was vapor-deposited on the Se deposit layer produced above. The resulting photosensitive member is called Sample A-2. A sample having a polyethylene terephthalate film adhered onto the Sample A-2 is called Sample B-2.

In a similar way, Se and a were deposited subsequently in a varying amount to form samples as shown in Table 1.

In Table 1 below, Sample A refers to a photosensitive member without an insulating layer while Sample B refers to that having a polyethylene terephthalate film on the surface. Examples of Sample A and Sample B are shown in FIG. 1 and FIG. 2, respectively, where a support, an Se deposit layer, an Se-Te alloy layer and an insulating layer are designated as 1, 2, 3 and 4.

Se g .1. Thickness of Se layer (micron) Sample A was charged with 6 kv. The charging curve is as shown in FIG. 3. In FIG. 3 and FIG. 4 the abscissa and the ordinate denote time and voltage, respectively. f and e denote an end of charging and a saturated surface potential, respectively.

Sample B was subjected to an electrophotographic process as mentioned above, that is, primary charging (f J secondary charging simultaneously with exposure (f f and blanket exposure (7;) as shown in FIG. 4. In the charging in FIG. 4 above, the primary charging was effected with -6 kv. and the secondary charging was ef fected with AC 6 kv. and further a light image was projected at 10 lux-sec. The curve a corresponds to the light portion and the curve b to the dark portion.

The charging potential of each sample in Table 1 is shown in Table 2. With respect to Sample A, a saturated surface potential e is indicated and with respect to Sample B, there is shown a contrast between the light and the dark portions.

TABLE 2 9 (-V.)..-.- 25 B Contrast (v.) 300 Measuring error of the values in Table 2 above is within It is generally considered that hole mainly serves as carrier for Se. When the Sample A is positively charged, the surface potential is sufliciently increased (over 500 v.), but the surface potential is saturated at a level lower than positive charge. It is considered that a carrier (hole) is injected from the support and bound with the negative charge on the surface. In view of this fact, it is clear with respect to Sample B having an insulating layer on the surface that injection of hole is excellent and rectifying ability is high and furthermore contrast is high.

As shown in Table 1, the Se vapor deposited layer facilitates sufiicient injection of hole, but the Se layer thicker than 5 microns lowers the sensitivity and high sensitivity of the Se-Te alloy layer is neither expected. Therefore, the resulting photosensitive member is not suitable for practical use.

On the contrary, when the thickness of Se layer is less than 0.01 micron, rectifying effect is not obtained. In other words, the layer is so thin that pin holes are formed and the Se-Te alloy layer directly contacts the support, and therefore, the Se layer does not serve as a rectifying layer.

With respect to the Se-Te alloy layer, as the Te content increases, the sensitivity increases and reaches the maximum sensitivity at about 20% by weight of Te and the resistance is also decreased, but crystallization is simultaneously accelerated and the life of the photosensitive member itself is shortened. Consequently, acceptable Te contents ranges from 6 to 45% by weight for maintaining the sensitivity at high level and preventing the crystallization. Thickness of the Se-Te alloy layer is preferably about 30-150 microns, particularly preferred with 30-90 microns for maintaining a desirable resistance and a sensitivity enabling rapid response.

As insulating layer, any insulating material may be used which is transparent to a radiation to which the photoconductor is sensitive. The desirable thickness of the insulating layer depends upon the mutual relation with the photoconductive layer, i.e. electrostatic capacity of the insulating layer and the photoconductive layer. Consequently, thickness of the insulating layer is determined by the Se-Te alloy layer. The thickness is preferably about 15-75 microns, particularly preferred with 15-45 microns.

We claim:

1. An electrophotographic photosensitive member comprising basically a conductive support, a photoconductive layer and an insulating layer, which comprises an Se rectifying layer being provided between said conductive support and said photoconductive layer, said rectifying layer being 0.01-5 microns in thickness and capable of injecting to the photoconductive layer a charge of a positive polarity from the side of said conductive support at the time of the application of a charge of a negative polarity, the photoconductive layer being of Se-Te containing 6-45 by weight of tellurium, being provided on said rectifying layer, said photoconductive layer being 30- microns in thickness and capable of binding said injected charge and expanding the photosensitivity region, and the insulating layer being provided on the photoconductive layer and having permeability to a radiation to which said Se-Te photoconductive layer is sensitive, said insulating layer being 15-75 microns in thickness and capable of retaining said applied charge of the negative polarity.

References Cited UNITED STATES PATENTS 3,708,291 1/ 1973 Kinoshita 961.5 3,355,289 11/1967 Hall et a1 96l.5 3,723,105 3/1973 Kitajima 961.5 2,962,376 11/1960 Schaffery 961.5

RONALD H. SMITH, Primary Examiner J. L. GOODROW, Assistant Examiner US. Cl. X.R. 96-1 PC 

